Meeting Abstract

38.5  Sunday, Jan. 5 09:00  Photoreceptors with dual sensitivity to UV and visible light are in the larval eyes of the basal arthropod Limulus polyphemus BATTELLE, B-A.*; KEMPLER, K.E.; PAYNE, R.; Whitney Lab. Univ. of Florida; Whitney Lab. Univ. of Florida; Univ. of Maryland, College Park battelle@whitney.ufl.edu

Limulus is a classic model for studies of vision. It has three types of eyes: lateral compound eyes (LE), median ocelli (ME) and lateral, median and ventral larval eyes. Larval eyes probably provide phototic information to embryos and newly hatched larvae: they contain both giant (150 µm long) and smaller (45 µm long) photoreceptors. Classic electrophysiological studies suggested all three eye types contain photoreceptors sensitive to visible light and only MEs contain photoreceptors sensitive to UV light. However, we showed that a UVopsin (LpUVops) is expressed in each eye type: in most ME photoreceptors; in LE eccentric cells, a cell type classically considered a second order neuron; and in small photoreceptors of the ventral larval eye (VE). Small VE photoreceptors also express LpOps5, a visible light sensitive opsin, suggesting they respond to both UV and visible (VIS) light. By contrast, giant VE photoreceptors only express visible light sensitive opsins. Intracellular recordings have now confirmed two spectral types of VE photoreceptors. One has spectral properties characteristic of giant VE photoreceptors with a major peak of sensitivity at 520nm and a minor peak at 360nm. The second type also has a peak at 520nm but an even larger peak at 360nm. This spectrum probably originates from small VE photoreceptors and indicates that both LpOps5 and LpUVops drive phototransduction in these cells, and that they are UV-VIS cells. In UV-VIS cells, maximum sensitivity at 520nm varies considerably relative to that at 360nm. This is consistent with immunocytochemical results showing that the rhabdomeral level of LpOps5 varies in a light-dependent manner while that of LpUVops does not. Thus the spectral tuning of the UV-VIS cells may change day to night.